1. Field of the Invention
This invention relates to improvements in a direct fuel injection type internal combustion engine having at least one combustion chamber fitted with a fuel injection valve for directly injecting fuel into the combustion chamber.
2. Description of the Prior Art
Internal combustion engines of the type having a combustion chamber fitted with a fuel injection valve for injecting fuel directly into the combustion chamber are well known. Such internal combustion engines may be Diesel engines which operate on heavy oil, or gasoline engines which use gasoline fuel. In the case of Diesel engines using heavy oil as a fuel, direct fuel injection is essential, because heavy oil cannot be vaporized or atomized in a conventional carburetor. In the case of gasoline being used as fuel, direct injection is an alternative to the use of a conventional carburetor. In either case, an engine using direct fuel injection has the notable advantage that it can be operated at a very lean air/fuel mixture ratio, such as one higher than 20:1, with a resulting improvement in fuel economy and emission of pollutants.
However, one of the difficulties encountered with such engines is a tendency for localized volumes of rich air/fuel mixture to be produced in the cylinder during fuel injection. As a result, during combustion, proper fuel combustion in these volumes does not occur, due to oxygen starvation, and emission of pollutants in the exhaust, as well as buildup of carbon deposits in the combustion chamber, greatly increases.